With Question 3 on the statewide ballot expected to pass Nov. 6, landlord groups say they want the right to turn away renters who are medical marijuana patients and those who may be authorized to cultivate marijuana. They don't want their apartments to become grow operations.

Federal law still forbids the use, sale or making of marijuana and may trump state law.

The ballot question asks to eliminate state penalties for marijuana use by qualifying patients, starting Jan. 1.

At present, 17 states and the District of Columbia allow medical marijuana.

Under the proposal, the state Department of Public Health would allow nonprofit medical marijuana treatment centers to grow, process and provide marijuana to patients or their caregivers. In 2013, there could be no more than 35 treatment centers, with at least one but not more than five in each county.

The landlords fear the “treatment center” could be in one of their units if the tenant attained the requisite state license to grow marijuana.

The grow operations, according to the proposal, would be in a “closed, locked facility” and provide a 60-day supply of marijuana for the patient's use.

In a worst-case scenario, the feds could step in and seize their properties for drug activity, the landlord advocates say.

Medical marijuana exposes the landlord to civil asset forfeiture under a federal law that allows police departments or the Department of Justice to take a private property that has been used in any way for drug activity, said Skip Schloming, executive director of the Small Property Owners Association in Cambridge.

“This puts the landlord in the vise of the conflicting legislation,” said Ron Bernard, editor of the Southern Worcester County Landlord Association's newsletter and chairman of its membership committee.

Mr. Bernard, who owns rental units in Southbridge and Warren, points out that a landlord can't discriminate against an existing or potential tenant because of a handicap or medical issue.

Mr. Bernard said his association, which has about 90 paid-up members, has concerns about the ballot question and hopes it will be defeated.

In case it passes, Mr. Schloming said, his organization is petitioning legislators to amend the proposal to remedy the landlords' concerns.

The landlords, Mr. Schloming said, want the cultivation of marijuana to be forbidden in homes and apartments and only be allowed in business settings.

Mr. Schloming said that because the ballot question allows growing to be done under lock and key, his organization anticipates landlords will have problems gaining access to their apartments in which a state-sanctioned grower is doing business.

He also noted that growing marijuana requires a lot of water, lighting and ventilation, and is widely known to put additional wear and tear on an apartment.

Mr. Schloming said the organization wants landlords to have the ability to turn down medical marijuana tenants or evict them, because such tenants are not likely to disclose this information to landlords.

Michael G. Gatlin, vice chairman of the Property Law Section of the Massachusetts Bar Association, said these are all legitimate concerns.

“At least at this point in time, it's hard to say what a landlord should do,” the Framingham lawyer said.

Mr. Gatlin said then Deputy U.S. Attorney General David Ogden sent a letter to U.S. attorneys in October 2009 saying that given the burgeoning nature of medical marijuana use, the agency would not prosecute people who are using marijuana in states where it's been made legal, nor were they going to prosecute caregivers.

But naturally, the government intends to prosecute trafficking, which in theory could be done by a caregiver, the lawyer said.

“It's an inconsistent kind of position,” said Mr. Gatlin, adding it would clearly be illegal for a federally financed or federally maintained housing project to allow people to grow marijuana on site.

“Beyond that, you're kind of hoping that the feds are going to look the other way, but there's no guarantee that they are,” he said.

Another concern, he said, is that medical marijuana would violate any type of mortgage a landlord would hold on the property. Every mortgage has language that says the property can't be used for illegal purposes.

“I think what's going to happen is, some unfortunate person is going to lose their property by way of a default under the mortgage for that reason, or the feds are going to seize it and test it in court,” Mr. Gatlin said.

“The bad news is you're going to have to litigate the issue, or there has to be some clarification to the statute that will result from this referendum that makes clear what the parties' rights are, at least under state law. The Legislature has to clean this thing.”

Morgan Fox, spokesman for the Washington, D.C.-based Medical Marijuana Project, said government interference with medical marijuana is “happening all over the country.”

The government, he said, leans on landlords to evict these tenants. It is to the chagrin of both providers and patients that some patients are no longer able to get safe, reliable access to their medicine.

“The only thing the federal government is doing when it tries to use this 'asset forfeiture' is it's just pushing the marijuana market underground where it can't really be licensed or controlled,” he said.

Landlords usually get a written warning and a certain amount of time to either challenge the proceedings or evict their tenants, he said.

The government claims “they aren't interfering with state medical marijuana laws, when in fact they are,” Mr. Fox said. They do it under a variety of guises, such as saying they're too close to schools, even though medical marijuana providers have shown no danger to children or to their communities in terms of increased violence or availability, Mr. Fox said.

Christina Sterling, a spokesman for the U.S. attorney's office in Boston, said her agency wouldn't comment on hypothetical scenarios.

But federal law, she said, unambiguously makes it unlawful to grow, distribute or possess marijuana, other than as part of a federally authorized research program.

Marijuana is a controlled substance and has been placed in Schedule 1 of the Controlled Substances Act, meaning it has no currently accepted medical use in the country and has not been determined to be safe and effective by federal health authorities, she said.

“While this office does not intend to focus its limited resources on seriously ill individuals who use marijuana as part of a medically recommended treatment program in compliance with state law,” she said, “individuals and organizations who are in the business of cultivating, selling or distributing marijuana and those who knowingly facilitate such activities will be in violation of federal law and subject to federal enforcement.”

If the Massachusetts ballot question passes, she added, her office will wait and see how the state will regulate marijuana.